import pygame
from pygame.sprite import Sprite
class Ship(Sprite):

    def __init__(self,ai_settings,screen):
        #初始化飞船并设置其初始位置
        super(Ship, self).__init__()
        self.screen=screen
        self.ai_settings = ai_settings

        #加载飞船图像并获取其外接矩形
        self.image=pygame.image.load('images/ship.bmp')
        self.rect=self.image.get_rect()
        self.screen_rect=screen.get_rect()

        #将每艘新飞船放在屏幕底部中央
        self.rect.centerx=self.screen_rect.centerx
        self.rect.bottom=self.screen_rect.bottom

        #在飞船的属性center中存储小数值
        self.center = float(self.rect.centerx)

        #移动标志
        self.moving_right=False
        self.moving_left=False

    def blitme(self):
        #在指定位置绘制飞船
        self.screen.blit(self.image,self.rect)

    def update(self):
        #根据移动标志调整飞船位置
        if self.moving_right and self.rect.right<self.screen_rect.right:
            self.center += self.ai_settings.ship_speed_factor
        if self.moving_left and self.rect.left>0:
            self.center -= self.ai_settings.ship_speed_factor

        self.rect.centerx = self.center

    def center_ship(self):
        self.center = self.screen_rect.centerx